Carrier wave telephone system



Nov. 28, 1939. J. J. A. PEEK. gr AL 2,181,457

' CARRIER WAVE TELEPHONE SYSTEM Filed Aug. v, 1931 Patented Nov. 28, 1939 UNITED STAT CARRIER' WAVE TELEPHONE SYSTEM Johannes Josephus Alphonsus Peek and Thomas Samuel Skillman, Eindhoven, Netherlands, assignors to N. V. Philips Gloeilampenfabrieken, Eindhoven, Netherlands Application August 7, 1937, Serial No. 158,002

' In Germany August 14, 1936 i, 1 Claim.

Our invention relates to four-wire carrier-Wave telephony transmitting systems in which the two speech directions kof a channel are transmitted through two pairs of conductors.

At the terminal stations of such systems, the above-mentioned pairs of conductors, which may form a singlev cable or two separate cables, terminate in a cable head, and each pair are connected from the cable head through a separateconnectprovided in the stations. 'Ihis arrangement, however, has the drawback that if one of the connecting lines becomes defective for some reason, all of the carrier wave channels passing therethrough will become inoperative. For example, in a twelve channel system, all of the channels will become defective if one of the connecting lines is interrupted. As it is frequently necessary, because of lack of room, to locate the carrierwave equipment at some distance from the cable head, these connecting lines are usually rather long which increases the possibility of damage thereto.

The object of our invention is to eliminate the above drawback in four-wire carrier-wave systems, in which different frequency bands are used for the transmission in the two speech directions of each channel.

According to the invention, we connectin at least one of the terminal stations-the two pairs of conductors of the four-wire transmitting system through suitable band-pass iilters to a common connecting line whose other end` is connected through filters to the modulator-demodulator circuit of the channel. In the case of a plurality of channels, we use a separate connecting line for each channel and connect each line through suitable lters to the pairs of conductors.

In order that the invention may be clearly understood and readilycarried into effect we shall describe same in more detail with reference to the accompanying drawing in which the single igureis a schematic wiring diagram of aterminal station of a transmitting system according to the invention.

The system illustrated comprises a pair of conductors L1 for the transmission in the direction of arrow a, and a pair of conductors L2 for the transmission in the direction of arrow b. In the terminal station, conductors L1 are connected to transmitting band-pass filters I0, II, and I2, and conductors L2 are connected to receiving band-pass filters 20, 2 I, and 22. The transmission range of filters I0, II, I2, 20, 2|, and 22 are so selected that each of them allows the passage only ing line to the usual carrier-wave equipment ofthe frequency band required for the transmission of a channel in one of the speech directions.

Furthermore, the transmission ranges of the y transmitting filters I0, II, and I2 are different from that of the corresponding receiving filters 20, 2I, and 22, so that the frequency bands are different for the two speech directions.

The output circuit of each transmitting bandpass filter and each receiving band-pass filter corresponding to the same channel are connected together and to a separate connecting line. More particularly, filters III-20, II-2I, and I2-22 are connected to connecting lines V1, V2, and V3 respectively. Consequently Athe conversation in one direction, and the conversation in opposite directionof each channel proceeds in the form of modulated carrier oscillations through each of these connecting lines, which oscillations, as has already been observed, require different frequency bands.

Due to the use of two different frequency bands for each channel, the two speech directions of each channel are separated by suitable filters 30-3I, 40-4I, and SI1-5I connected at ends of connecting vlines V1, V2, and V3, respectively. Filters 30, 40, and 5l), are connected to modulators 32, 42, and 52 respectively, whereas iilters 3|, 4I, and 5I are connected to demodulators 33, 43, and 53 respectively. Modulator 32 and demodulator 33 are connected through low-pass 30 filters 34 and 35 respectively'and balancing appai ratus 36 to low-frequency transmitting lines T1, whereas modulator 42 and demodulator 43 are connected through low-pass filters 44 and 45 respectively and a balancing apparatus 46 to lowfrequency lines T2. In a similar manner modulator 52 and demodulator 53 are connected through low-pass filters 54 and 55 respectively and balancing apparatus 56 to low-frequency lines Ts.

From the above it is seen that each of the connecting lines V1, V2, and V3 is used for only one channel, and that if one of these lines is interrupted only one channel will be made inoperative, while communication through the remaining channels will be unaffected.

While we have described our invention in connection with a specific example we do not wish to be limited thereto, but desire the appended claim to be construed as broadly as permissible in r view of the prior art.

What we claim is:

In a multi-channel carrier-wave transmission system, a pair of conductors for transmitting modulated carrier-waves in one direction, a secl ond pair of conductors for transmitting modulated carrier-waves in the opposite direction, a common connecting line for each channel, two band-pass lters for each channel, one of said lters having its input connected to said first pair of conductors and its output connected to the corresponding connecting line and the second of said lters having its `output connected to said second pair of conductors and its input connected to the corresponding connecting line, the two filters of each channel having.Y transmission ranges which differ from each other and from the transmission ranges of the filters of the other channels, a modulator for each channel comprising a lter, and a demodulator for each channel comprising a filter, the output circuit of the modulator :filter and the input of the demodulator filter for each channel. being connected. to the other end of the connecting line corresponding to the channel.

JOHANNES J OSEPHUS ALPHONSUS PEEK.

THQMASSAMUEL SKILLMAN. 

